A solar technician is troubleshooting a newly installed string inverter that is frequently disconnecting due to a 'Grid Undervoltage' error, even when the utility grid voltage appears stable. The system is operating at full power. What is the most likely cause of this issue?
- AThe PV modules are experiencing severe partial shading.
- BThe utility grid is experiencing frequent transient overvoltages.
- CThe AC conductors between the inverter and the point of interconnection are undersized.
- DThe inverter's internal voltage sensors are faulty.
Show answer & explanationAnswer & explanation
Correct answer: C. The AC conductors between the inverter and the point of interconnection are undersized.
When an inverter pushes current through undersized AC conductors, it creates a significant voltage drop. This voltage drop means that the voltage at the inverter's AC terminals will be lower than the actual utility grid voltage, potentially causing the inverter to incorrectly detect a 'Grid Undervoltage' condition and disconnect, even if the utility grid itself is stable. This is a common issue with voltage rise/drop in PV systems.
Why the other options are wrong
- A. Severe partial shading would reduce power output, not typically cause a 'Grid Undervoltage' error.
- B. Transient overvoltages would lead to 'Grid Overvoltage' errors, not 'Grid Undervoltage'.
- D. While possible, faulty sensors are less likely than a common installation issue like conductor sizing.
Inverter Voltage Drop (AC Side)
The reduction in voltage between the inverter's AC output and the utility grid's point of interconnection, primarily due to resistance in the AC conductors.
- Can cause inverters to trip on undervoltage or overvoltage (voltage rise).
- Leads to reduced system performance and energy harvest.
- Mitigated by properly sizing conductors for current and distance.
Memory trick: Thin wires make voltage low, causing the inverter to disconnect and go!